1. Field
Aspects relate to an image forming apparatus and a method for color registration correction, and more particularly, to an image forming apparatus which can swiftly adjust an amount of light of a registration sensor, which examines an image alignment of the image forming apparatus, in a feedback manner, and a method for color registration correction.
2. Description of the Related Art
An electrophotographic printer such as a color laser printer includes four organic photo conductors Dy, Dc, Dm, and Dk prepared to respond to four colors, yellow, cyan, magenta, and black, a laser scanning unit to scan each of the organic photo conductors Dy, Dc, Dm, and Dk with a laser to form an electrostatic latent image of a desired image, a developing apparatus to develop the electrostatic latent image with color developers, and a transfer belt (or an intermediate transfer belt) to receive images developed on the organic photo conductors Dy, Dc, Dm, and Dk in sequence such that the images overlap with one another to form a complete color image, and transfer the color image to paper.
Accordingly, in order to print a desired single color image, the printer develops images for respective colors on the four organic photo conductors Dy, Dc, Dm, and Dk, moves the images to the same position of the transfer belt to make them overlap with one another to form a final color image, and transfer the final color image to paper.
However, in order to form the desired color image correctly by making the four colors overlap with one another at the same position on the transfer belt, transfer of the four color images from the organic photo conductors Dy, Dc, Dm, and Dk to the transfer belt should begin at the same position and ends at the same position on the transfer belt. Even if all images are clearly developed on the four organic photo conductors Dy, Dc, Dm, and Dk, a slight misalignment of the images on the transfer belt may cause a problem that a finally obtained color image does not correctly represent a color and an image.
Therefore, in order to represent a color image correctly, it is important to match a laser scanning time of the laser scanning unit for each organic photo conductor Dy, Dc, Dy, and Dk in consideration of a traveling speed of the transfer belt. A technique of matching the laser scanning time to make a plurality of colors overlap with one another to form a single image is referred to as ‘color registration’.
The color registration is performed using a registration sensor provided in the image forming apparatus. The registration sensor projects light onto a registration pattern developed on an image forming medium and senses light reflected from the registration pattern, thereby measuring an error in alignment of images.
In order to measure the error in the alignment of the images accurately, the registration sensor should project light onto the image forming medium based on a correct amount of light.
More specifically, if an amount of light of the registration sensor is greater than a predetermined value, some of the registration patterns developed on the transfer belt may not be recognized. If the amount of light of the registration sensor is less than the predetermined value, contamination on the transfer belt may be recognized as a pattern.
In a related-art method for detecting an amount of light of the registration sensor, a PWM duty is input to the registration sensor in a stepwise manner, and, when the amount of light reaches a target amount of light according to a change in the PWM duty, the amount of light by the corresponding PWM duty is used for color registration.
However, the related-art method requires long time to detect the amount of light of the registration sensor because a series of operations of changing the PWM duty in sequence should be performed.
Also, the amount of light of the registration sensor may not be detected since the target amount of light falls between the PWM duty steps in the case of an image forming apparatus of high reflectivity.